Typically, a navigation device (be that an in-vehicle navigation device (i.e. a device built into a vehicle that cannot be removed from that vehicle), a PND such as a TomTom® Go 720, or a mobile telephone, personal digital assistant (PDA) or computer executing navigation software) is configured to display an image consisting of a map view generated from a digital map. The map view may be superposed with route information depicting a navigation route, and whilst the route information may be pre-recorded, but it is typically the result of a route-planning algorithm executed by the navigation device using suitable software. The navigation device may also include a position determining system (such as Global Positioning System (GPS)) for determining the current real-time position of the navigation device, and for dynamically adjusting the map view in accordance with the determined current position.
A popular type of map view is a two-dimensional-based map view that includes information in two-dimensions at ground level. For example, roads and buildings are represented by the shape of their footprints on the ground. Such two-dimensional information may be viewed as a plan (i.e. looking generally vertically downwardly on the map, in the same manner as a traditional paper map), or in artificial perspective as if viewing a traditional flat paper map from a perspective angle. However, in either case, the map view is generally “flat” in the sense that the information is only two-dimensional ground level information. References hereafter to a two-dimensional plan view should be construed to include both of these types of map view.
A further type of map view is a three-dimensional elevated perspective view, similar to an artificial perspective view but including three-dimensional rendering according to height information of map objects. For example, a building is rendered in three-dimensions according to height information for the building.
In the context of in-vehicle use, it is generally desirable to provide a highly intuitive navigation display that (i) provides the driver with current navigation information, and (ii) provides an indication of the future route, so that driver can drive and position the vehicle appropriately.
It has also been previously proposed to provide other information to the driver that could potentially be of use. For example, it has previously been proposed to display points of interest (such as banks, petrol stations or public facilities) that are on or close to the route, street names for roads on or close to the route, and icons representing the location of speed limit enforcement cameras that are on the chosen route.
Whilst the provision of these additional items of information can often be of use to the driver, it is important that the driver is not overburdened with information so that the route becomes difficult to follow, or the map difficult to read, or the driver distracted by the amount of information displayed. This applies to both two-dimensional and three-dimensional map views, but is especially apparent in a three-dimensional perspective elevation, in which the map view contains additional detail in the form of three-dimensional shapes of map objects such as buildings.
Clearly there is a fine balance to be drawn between providing the driver with information that might be of use and not overburdening the display image with information to such an extent that the driver's attention is distracted from safely operating the vehicle in which the PND is provided, and the present invention has been devised with the aim of addressing these contradictory issues.